In general, Etch-like effect is referred to an optical effect resulting from non-smooth surface structure and morphology. The original art of Etching is referred to an intaglio method of printmaking in which the image is incised into the surface of a metal plate using an acid. The acid causes etching of predetermined parts of the substrate surface, thus giving a surface with various heights, bringing a unique optical appearance. A similar effect can be achieved by etching glass with suitable chemicals, or by mechanical coarsening of the glass surface, for example by sand blasting.
Commercial product for screen printing for providing etch-like effect on glass surfaces are available, the etch-like effect is achieved by creating a surface roughness, which is obtained by presence of particles having an average particle size above several micron. Such products are also highly viscous, since they contain high concentration of the particles. These two features are suitable for conventional screen printing, however, they are not suitable for ink jet printing.
Ceramic materials are hard, brittle, heat- and corrosion-resistant substrates made by shaping and then heating a non-metallic mineral, such as clay, at a high temperature. Enamels, porcelain, and bricks are examples of materials that are produced by molding or shaping minerals and baking or firing them at high temperatures.
Glass products are typically made by fusing silicates with boric oxide, bismuth oxide aluminum oxide or phosphorus pentoxide at high temperatures. They have highly variable mechanical and optical properties and solidify from the molten state without crystallization into a transparent or translucent form. While glass items are generally hard and brittle, their lack of crystalline structure puts them in the class of amorphous solids. Glass items that may require printed graphics include windows, mirrors, cooking utensils, bottles, containers, and more.
From a printing point of view, several methods are available for decorating glass and ceramics with high-quality images. The printing processes used for glass and ceramic printing rely on a variety of ink systems. Most inks fall into one of two families: organic and inorganic.
Organic inks are typically used in screen, inkjet and pad printing, and consist of organic pigments and resins along with other chemistries that cure over time and rely on temperature or some other form of energy to create a bond with the substrate. The most effective organic inks are produced as two-component or two-part systems. These inks generally contain resins capable of polymerization that are blended with catalysts to initiate polymerization.
Inorganic inks use mineral-based pigments and materials that, once printed, have to be heated and melted at high temperatures in order to combine with the substrate surface and form a permanent bond. However, it is expected that the organic ink components will be burnt out at high temperature.
Ceramic colors, as inorganic ceramic inks are called, are a mixture of pigments (metal oxides and salts) and finely ground glass particles, called frit. These materials are fused to the substrate by calcining (“firing”) them at temperatures between 600-1450° C. Firing temperatures vary depending on the make-up of the color, the nature of substrate, and other application criteria, but in all cases the temperatures must be carefully controlled to achieve specific colors after firing.
These high firing temperatures are used as the components of ceramic colors need to be melted so they can fuse to the ceramic surface on which they are printed. While these inks are typically called “inorganic”, they may also contain small amounts of organic material. The organic components are the materials in which the pigment and frit are suspended to create a printing ink. These organic materials, which are oily in nature, are designed to bum off rapidly during firing without affecting print quality and final color.
While printing on ceramic surfaces with inorganic inks may be obtained by silk-screen, pad printing or digital printing, commercial ceramic inks are difficult to use in inkjet printing as they have typically a viscosity higher than required for inkjet printing (about 20-40 cP) and the glass frit contained in them, which is in the micron size range, tends to sediment and also clog the nozzles on the orifice plate from which the ink is jetted during inkjet printing.
An ink composition containing pigments, which is liquid at room temperature for printing on a ceramic substrate to be fused to the substrate upon firing is described in WO2005/019360.
There is a widely recognized need for and it would be highly advantageous to have an ink-jet ink composition which is liquid for use in ink-jet printers and which can provide an etch-like effect instead of traditional screen printing compositions.
It would have been highly desirable to use inkjet printing on the ceramic surfaces with ceramic sub -micron particles imparting the Etch-like effect, instead of the currently used methods of silk-screen printing.
The objective of the present invention is to achieve the etch-like effect by digital printing, namely ink jet printing, on ceramic surfaces, mainly glass surfaces while utilizing novel ink jet inks.
Converting to digital printing can have the following advantages: reduction of costs involved with storage of screens or transfer devices due to digital storing of the desired patterns instead of physical storage; reduction of costs for low volume printing which can be prohibitive in silk-screen printing; increase the ease and versatility of switching from one design to another, capacity for edge to edge printing utilization.